Explanation:

Relational algebra is a mathematical query language used to manipulate the relational database. It consists of a set of operations that can be applied on relations (tables) to produce another relation as a result. These operations are based on set theory and provide a way to retrieve, modify, and combine data in a relational database.

Commutative operation is an operation that produces the same result regardless of the order of the operands. In other words, the order of the operands does not matter in commutative operations.

Now let's analyze each option to determine which one is not a commutative operation.

1. Union: The union operation combines two relations and returns a new relation that contains all the tuples from both relations, removing any duplicates. The order of the operands does not matter in the union operation, and it produces the same result regardless of the order. Therefore, union is a commutative operation.

2. Intersection: The intersection operation returns a new relation that contains only the common tuples between two relations. Like the union operation, the order of the operands does not matter in the intersection operation, and it produces the same result regardless of the order. Therefore, intersection is a commutative operation.

3. Selection: The selection operation filters the tuples of a relation based on a given condition and returns a new relation that contains only the selected tuples. The order of the operands does not matter in the selection operation, and it produces the same result regardless of the order. Therefore, selection is a commutative operation.

4. Projection: The projection operation selects specific attributes (columns) from a relation and returns a new relation with only those attributes. Unlike the other operations, the order of the operands does matter in the projection operation. Changing the order of the attributes in the projection operation will result in a different relation with different attribute order. Therefore, projection is not a commutative operation.

Conclusion: The relational algebraic operation that is not a commutative operation is Projection (option D).